How to use
- Paste the Base64 string or the data:image/avif;base64 URI.
- Check the preview, the detected format and the dimensions.
- To save an AVIF unchanged, choose Original. To convert another format, keep AVIF selected; if your browser cannot encode AVIF, the option is unavailable.
- Download the .avif file.
What AVIF data looks like
AVIF stores an image compressed with the AV1 video codec inside a HEIF container, the same ISO base media file structure used by MP4. There is no short fixed signature like PNG's. Instead the file opens with an ftyp box that names the brand avif, or avis for animated sequences. In Base64 that usually means the string starts with AAAA and contains eXBhdmlm a few characters later. The tool reads the box itself, so it can tell AVIF apart from HEIC, which uses the same container with a different brand. The MIME type is image/avif.
Converting to AVIF depends on your browser
Current versions of Chrome, Edge, Firefox and Safari all display AVIF, so previewing and saving the original file works almost everywhere. Creating new AVIF files is different. The conversion uses the encoder built into your browser, and not every browser can produce AVIF from a canvas. The tool checks whether yours can. If it cannot encode AVIF, the option is unavailable, and WebP is the closest alternative. You can also download a PNG and encode it with a dedicated tool such as avifenc from libavif.
When AVIF is worth it
AVIF often beats JPEG and WebP on file size at the same visual quality, especially for photos, and it supports transparency, high bit depth and HDR. Encoding is slower, and some older image editors and operating systems still cannot open it. For very small images such as icons, the container overhead can cancel out the gains, so PNG or WebP may come out smaller. On websites, serve AVIF with a fallback so every visitor sees an image:
<picture>
<source srcset="photo.avif" type="image/avif">
<img src="photo.jpg" alt="Description">
</picture>Frequently asked questions
Why is the AVIF download option unavailable?
Your browser can display AVIF but cannot encode it from a canvas. Try another up-to-date browser, choose WebP instead, or download a PNG and convert it with a desktop encoder.
Why does my AVIF not show a preview?
An older browser or operating system may not decode AVIF. The data might also be HEIC, which looks similar but uses a different brand; the detected format tells you which one it is. Downloading as Original works in either case.
Is AVIF always smaller than WebP?
Often, but not always. Results depend on the image and the encoder settings, so compare the downloaded file sizes.